Field
Anaerobic curable compositions, such as adhesives and sealants, containing blocked dicarboxylic acid compounds are provided. The blocked dicarboxylic acid compounds are labile dicarboxylic acid compounds having two acetal linkages, which cleave to release the underlying dicarboxylic acid during anaerobic cure. In this way, the dicarboxylic acid can participate in the anaerobic cure of the composition when the blocking group is released.
Brief Description of Related Technology
Anaerobic adhesive compositions generally are well-known. See e.g., R. D. Rich, “Anaerobic Adhesives” in Handbook of Adhesive Technology, 29, 467-79, A. Pizzi and K. L. Mittal, eds., Marcel Dekker, Inc., New York (1994), and references cited therein. Their uses are legion and new applications continue to be developed.
Conventional anaerobic adhesive compositions ordinarily include a free-radically polymerizable acrylate ester monomer, together with a peroxy initiator and an inhibitor component. Oftentimes, such anaerobic adhesive compositions also contain accelerator components to increase the speed with which the composition cures. Additionally, such compositions may also include adhesion promoters, which can function to increase adhesion to substrates, thereby enhancing adhesive strength.
Maleic acid (“MA”) is a commonly used accelerator, together with acetyl phenylhydrazine (“APH”), in anaerobic adhesive compositions. However, MA has limited solubility in some of these compositions, a prime example of which is LOCTITE 243, commercially available from Henkel Corporation, Rocky Hill, Conn.
In addition to its solubility limits, MA has the disadvantage of being heavily regulated due to its health and safety profile, and thus, requires special considerations during handling, storage, and disposal.
As a result of its limited solubility and regulatory scrutiny in certain parts of the world, efforts have been undertaken to identify replacements for MA. To date, these efforts have not provided an acceptable alternative.
It would thus be advantageous to enjoy the properties conferred upon anaerobic curable compositions by MA without the attendant environmental and safety concerns and sparing solubility properties. The present invention provides such a solution.